JP7179132B2 - insulated wire - Google Patents

Description

The present invention relates to insulated wires.

2. Description of the Related Art In insulated wires used for coils of motors and the like, an insulating layer covering a conductor is required to have excellent insulating properties, adhesion to the conductor, heat resistance, mechanical strength, and the like. Synthetic resins used for forming this insulating layer include, for example, polyimide, polyamideimide, and polyesterimide.

In addition, in electrical equipment with a high applied voltage, such as a motor that is used at a high voltage, a high voltage is applied to the insulated wires that constitute the electrical equipment, and partial discharge (corona discharge) is likely to occur on the surface of the insulation layer. . When corona discharge occurs, it tends to cause a local rise in temperature and the generation of ozone, etc. As a result, the insulation layer of the insulated wire deteriorates, causing early dielectric breakdown and shortening the life of electrical equipment. Insulated wires to which a high voltage is applied are required to have an improved corona discharge initiation voltage for the above reasons, and it is known that lowering the dielectric constant of the insulating layer is effective for this purpose.

Furthermore, the insulated wire may be exposed to a moist and hot environment. Under such an environment, the synthetic resin forming the insulating layer is hydrolyzed and its molecular weight is remarkably lowered, and as a result, cracks or the like may occur and the function as an insulating layer may be deteriorated. Therefore, the insulating layer of the insulated wire is sometimes required to have the performance (wet heat deterioration resistance) of suppressing the functional deterioration in the moist heat environment.

Furthermore, when an insulated wire is used as a coil, the insulated wire is bent in order to increase the space factor of the coil. Specifically, for example, after forming a coil by winding an insulated wire, the coil is inserted into a slot, or pre-deformed insulated wires are welded together to form a coil. The insulating layer of the insulated wire used for such applications is required to have bending workability that suppresses the occurrence of cracks, pinholes, voids, and the like that cause deterioration of electrical properties when bent.

Among the synthetic resins used for the insulating layer of insulated wires, polyimide has particularly excellent heat resistance, low dielectric constant, and excellent mechanical strength. It is used for the insulation layer of insulated wires used at high voltages because it can achieve excellent bending workability. For example, in JP-A-2013-253124, a resin containing a polyimide precursor which is a reaction product of an aromatic diamine and an aromatic tetracarboxylic dianhydride and has an imide group concentration within a specific range after imidization It is described that by forming an insulating layer using a varnish, an insulated wire that is excellent in heat resistance and crazing resistance and resistant to corona discharge can be obtained.

JP 2013-253124 A

However, since polyimide is a material that may be hydrolyzed when exposed to a moist and hot environment for a long time, the insulating layer of the conventional insulated wire has room for improvement in terms of resistance to moist and heat deterioration.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an insulated wire having an insulating layer with excellent bending workability and moisture-heat deterioration resistance.

An insulated wire according to one aspect of the present invention, which has been made to solve the above problems, is an insulated wire comprising a conductor and one or more insulating layers laminated on the outer peripheral side of the conductor, wherein the insulating layer At least one of the layers is mainly composed of polyimide derived from the reaction product of aromatic tetracarboxylic dianhydride and aromatic diamine, and when immersed in N-methyl-2-pyrrolidone at 80 ° C. for 4 hours The degree of mass swelling is 1.3 times or more and 20.0 times or less, the aromatic tetracarboxylic dianhydride contains biphenyltetracarboxylic dianhydride, and the aromatic tetracarboxylic dianhydride is 100 mol% The content of biphenyltetracarboxylic dianhydride is 25 mol % or more and 95 mol % or less.

The insulated wire according to one aspect of the present invention is excellent in bending workability and resistance to moisture-heat deterioration of the insulating layer.

[Description of the embodiment of the present invention]
An insulated wire according to one aspect of the present invention is an insulated wire including a conductor and one or more insulating layers laminated on the outer peripheral side of the conductor, wherein at least one of the insulating layers is an aromatic The polyimide derived from the reaction product of tetracarboxylic dianhydride and aromatic diamine is the main component, and the mass swelling degree when immersed in N-methyl-2-pyrrolidone (NMP) at 80 ° C. for 4 hours (hereinafter Also referred to as "NMP mass swelling degree") is 1.3 times or more and 20.0 times or less, the aromatic tetracarboxylic dianhydride includes biphenyltetracarboxylic dianhydride, and the aromatic tetracarboxylic dianhydride The content of biphenyltetracarboxylic dianhydride is 25 mol% or more and 95 mol% or less with respect to 100 mol% of the anhydride.

Since the insulated wire has the above configuration, the insulating layer is excellent in bending workability and resistance to moisture-heat deterioration. Although it is not clear why the insulated wire having the above structure provides the above effect, it is presumed as follows. That is, at least one of the one or more insulating layers of the insulated wire is mainly composed of polyimide derived from a polyimide precursor using a specific amount of BPDA, which is difficult to hydrolyze, as a raw material. Since this polyimide contains a specific amount of a structure that is difficult to hydrolyze derived from BPDA, it is difficult to be hydrolyzed even in a hot and humid environment, so it is thought that the resistance to wet heat deterioration of the insulating layer is improved. In the insulated wire, the NMP mass swelling degree of the insulating layer is within the above range, that is, the insulating layer is a layer that is appropriately swollen by a resin varnish solvent represented by NMP, so that the insulating layer Bending workability can be improved for the following reasons while suppressing a decrease in solvent resistance.

That is, when forming an insulating layer containing polyimide as a main component, a coating step of applying a resin varnish containing a polyimide precursor (polyamic acid) to the outer peripheral side of the conductor, and a heating of heating the resulting coating film It is common to use a method comprising the steps of: In the above method, only a relatively thin insulating layer of about several μm can be formed in a single coating step and heating step. A plurality of insulating layers are sequentially laminated. When the solvent such as NMP contained in the resin varnish slightly dissolves the polyimide contained in the base layer (insulating layer formed in the previous coating process and heating process) during the second and subsequent coating processes, It is thought that the base layer and the newly laminated insulating layer become more compatible with each other, so that the adhesion between the respective layers is improved. Here, when the insulating layer corresponding to the base layer is a layer that is moderately swollen by a resin varnish solvent represented by NMP, the infiltration of the resin varnish solvent into this insulating layer accelerates the dissolution of the polyimide. Therefore, it is considered that the underlayer and the newly laminated insulating layer become more compatible with each other, and as a result, the adhesion between the respective layers can be improved more reliably. As a result, when the insulating layer of the insulated wire is greatly deformed by bending or the like, it is possible to suppress the deterioration of the insulating properties, etc. due to the separation of each layer of the insulating layer, so the bending workability of the insulating layer It is considered to be superior to NMP is a typical resin varnish solvent, and since polar solvents similar to NMP are often used in resin varnishes, the insulating layer, which tends to swell due to NMP, cannot be washed with a resin varnish solvent other than NMP. It is also considered that it is easy to swell. Therefore, even when the insulating layer of the insulated wire is formed of a resin varnish containing a solvent other than NMP, the above-described effect of improving bending workability can be obtained.

Here, the degree of NMP mass swelling of the insulating layer is considered to be determined by the type of polyimide that is the main component of the insulating layer and the formation conditions of the insulating layer. Then, when the structure derived from BPDA is excessively introduced into polyimide, the biphenyl structure of BPDA promotes packing between molecules, making it difficult for solvents such as NMP to penetrate between molecules, and the NMP mass swelling degree is reduced. It is thought that there is a possibility that it will decrease. Therefore, in the insulated wire, the content of BPDA in the raw material of the polyimide precursor is set to the above upper limit or less, that is, by appropriately introducing a structure derived from BPDA into the polyimide, the NMP mass swelling degree can be easily and reliably increased. It can be within the above range. Here, the “main component” is the component with the highest content, for example, a component with a content of 50% by mass or more. The "NMP mass swelling degree" is R1 (g) for the total mass of the insulating layer after the NMP swelling treatment, and R2 (g) for the mass after drying the insulating layer after the NMP swelling treatment at, for example, 200 ° C. for 1 hour. The value expressed by the following formula when
NMP mass swelling degree (times) = R1/R2

The aromatic tetracarboxylic dianhydride preferably further contains pyromellitic dianhydride. In this case, the content of pyromellitic dianhydride with respect to 100 mol% of the aromatic tetracarboxylic dianhydride is 5 mol % or more and 75 mol % or less is preferable. In this way, by including a specific amount of pyromellitic dianhydride in the aromatic tetracarboxylic dianhydride, a rigid structure can be introduced into the polyimide, so that the heat resistance of the insulating layer can be improved.

The aromatic diamine preferably contains diaminodiphenyl ether. Thus, the toughness of the insulating layer can be improved by including the diaminodiphenyl ether in the aromatic diamine.

[Details of the embodiment of the present invention]
An insulated wire according to one aspect of the present invention will be described below.

<Insulated wire>
The insulated wire includes a conductor and one or more insulating layers laminated on the outer peripheral side of the conductor. The insulated wire is excellent in bending workability of the insulating layer and resistance to moisture-heat deterioration.

[conductor]
As a material for the conductor of the insulated wire, a metal having high electrical conductivity and high mechanical strength is preferable. Examples of such metals include copper, copper alloys, aluminum, nickel, silver, soft iron, steel, and stainless steel. The conductor of the insulated wire is made of a linear material of any of these metals, or of a multi-layered structure in which such a linear material is further coated with another metal, such as nickel-coated copper wire, silver-coated copper wire, A copper-coated aluminum wire, a copper-coated steel wire, or the like can be used.

The lower limit of the average cross-sectional area of the conductor of the insulated wire is preferably 0.01 mm ² , more preferably 0.1 mm ² . On the other hand, the upper limit of the average cross-sectional area of the conductor is preferably 10 mm ² , more preferably 5 mm ² . If the average cross-sectional area of the conductor is smaller than the lower limit, the resistance value may increase. Conversely, if the average cross-sectional area of the conductor exceeds the upper limit, the insulating layer must be formed thick enough to sufficiently lower the dielectric constant, and the insulated wire may unnecessarily increase in diameter. .

[Insulating layer]
One or more insulating layers of the insulated wire are laminated on the outer peripheral side of the conductor. When the insulated wire has a plurality of insulating layers, the insulating layers are sequentially laminated concentrically on the outer peripheral side of the conductor in a cross-sectional view. In this case, the average thickness of each insulating layer can be, for example, 1 μm or more and 5 μm or less. Further, the average total thickness of the plurality of insulating layers can be, for example, 10 μm or more and 200 μm or less. Furthermore, the total number of insulating layers can be, for example, 2 to 200 layers.

At least one of the plurality of insulating layers is mainly composed of a polyimide derived from a polyimide precursor (polyamic acid) that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, and contains 80% NMP. The degree of mass swelling when immersed at °C for 4 hours is 1.3 times or more and 20.0 times or less.

The lower limit of the NMP mass swelling degree of the insulating layer is preferably 1.35 times, more preferably 1.4 times. On the other hand, the upper limit of the NMP mass swelling degree is preferably 15.0 times, more preferably 7.0 times, and still more preferably 3.0 times. If the NMP mass swelling degree is less than the lower limit, the interlayer adhesion of the insulating layer cannot be sufficiently improved, and as a result, the bending workability of the insulating layer may deteriorate. Conversely, if the NMP mass swelling degree exceeds the upper limit, the insulating layer may have reduced solvent resistance.

The degree of NMP mass swelling of the insulating layer can be controlled by the type of polyimide, which is the main component, and the method of forming the insulating layer. As a method of controlling the degree of NMP mass swelling depending on the type of polyimide, for example, a method of introducing a structure with a high molecular weight into the polyimide to reduce the proportion of imide groups, or a method of making the molecular weight of the polyimide moderate, that is, A method using a polyimide precursor having an appropriate weight-average molecular weight for forming the polyimide can be used. In addition, as a method of adjusting the degree of NMP mass swelling by the method of forming the insulating layer, for example, a method of preventing the formation of a crystal structure in the polyimide can be mentioned. Specific conditions for each method will be described later.

(polyimide precursor)
The polyimide precursor, which is the raw material of the polyimide, is a polymer that forms a polyimide by imidization, and is a reaction product obtained by polymerization of an aromatic tetracarboxylic dianhydride and an aromatic diamine. That is, the above polyimide precursor is made from an aromatic tetracarboxylic dianhydride and an aromatic diamine.

As a minimum of the weight average molecular weight of the said polyimide precursor, 10,000 is preferable and 20,000 is more preferable. Moreover, as an upper limit of the said weight average molecular weight, 100,000 is preferable and 80,000 is more preferable. If the weight average molecular weight is less than the lower limit, the insulating layer may have insufficient mechanical strength. Conversely, if the weight-average molecular weight exceeds the upper limit, the coating properties of the resin varnish used to form the insulating layer may deteriorate, and as a result coating defects may occur in the insulating layer. In addition, an increase in the molecular weight of the formed polyimide promotes intermolecular interaction, which may make it difficult for a solvent such as NMP to permeate the molecules. As a result, the NMP mass swelling degree of the insulating layer may decrease, and the bending workability may decrease. Here, the "weight average molecular weight" refers to JIS-K7252-1: 2008 "Plastics-Method for determining the average molecular weight and molecular weight distribution of a polymer by size exclusion chromatography-Part 1: General rules", gel permeation It refers to values measured using chromatography (GPC).

The molar ratio of the aromatic tetracarboxylic dianhydride and the aromatic diamine (aromatic tetracarboxylic dianhydride/aromatic diamine) used as raw materials for the polyimide precursor is from the viewpoint of ease of synthesis of the polyimide precursor. Therefore, it can be, for example, 95/105 or more and 105/95 or less.

(Aromatic tetracarboxylic dianhydride)
The aromatic tetracarboxylic dianhydride used as a raw material for the polyimide precursor contains BPDA. BPDA includes 3,3′,4,4′-biphenyltetracarboxylic dianhydride (3,3′,4,4′-BDPA), 2,3,3′,4′-biphenyltetracarboxylic dianhydride anhydride (2,3,3′,4′-BDPA), 2,2′,3,3′-biphenyltetracarboxylic dianhydride (2,2′,3,3′-BDPA) and the like. , and among these, 3,3′,4,4′-BDPA is preferred.

The lower limit of the content of BPDA with respect to 100 mol % of the aromatic tetracarboxylic dianhydride is 25 mol %, preferably 35 mol %, more preferably 55 mol %. On the other hand, the upper limit of the BPDA content is 95 mol %, preferably 92 mol %. By setting the content of the BPDA in the above range, it is possible to appropriately introduce a structure derived from BPDA into the polyimide, which is the main component of the insulating layer, and as a result, bending workability and resistance to moist heat deterioration are well balanced. can improve. If the content of BPDA is less than the above lower limit, the resistance to moisture and heat deterioration of the insulating layer may deteriorate. Conversely, when the content of BPDA exceeds the upper limit, that is, when a structure derived from BPDA is excessively introduced into polyimide, the biphenyl structure possessed by BPDA promotes packing between polyimide molecules, and solvents such as NMP It may become difficult to permeate between molecules. As a result, the NMP mass swelling degree of the insulating layer may decrease, and the bending workability may decrease.

Among the aromatic tetracarboxylic dianhydrides used as raw materials for the polyimide precursor, aromatic tetracarboxylic dianhydrides other than BPDA include, for example, pyromellitic dianhydride (PMDA), 3,3′,4 ,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-oxydiphthalic dianhydride, 2,2′,3,3′-benzophenonetetracarboxylic dianhydride, 2,2-bis( 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride , 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3, 6,7-naphthalenetetracarboxylic dianhydride and the like. The other aromatic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

The aromatic tetracarboxylic dianhydride used as a raw material for the polyimide precursor preferably further contains PMDA or BTDA. By using PMDA having a rigid structure as a raw material for the polyimide precursor, a rigid structure can be introduced into the polyimide after imidization, so that the heat resistance of the insulating layer can be improved. Moreover, by using BTDA, which has a relatively large molecular weight, as a raw material for the polyimide precursor, the NMP mass swelling degree can be appropriately increased, and as a result, the bending workability of the insulating layer can be further improved. Note that PMDA and BTDA may be used in combination.

The lower limit of the PMDA content relative to 100 mol % of the aromatic tetracarboxylic dianhydride used as the starting material for the polyimide precursor is preferably 5 mol %, more preferably 8 mol %. On the other hand, the upper limit of the PMDA content is preferably 75 mol%, more preferably 65 mol%, still more preferably 45 mol%, and even more preferably 20 mol%. If the PMDA content is less than the lower limit, the heat resistance of the insulating layer may be insufficient. Conversely, if the content of PMDA exceeds the upper limit, the structure derived from BPDA cannot be sufficiently introduced into polyimide, which is the main component of the insulating layer, and as a result, the insulating layer is resistant to moisture and heat deterioration. may decrease.

The lower limit of the BTDA content relative to 100 mol % of the aromatic tetracarboxylic dianhydride used as the starting material for the polyimide precursor is preferably 5 mol %, more preferably 30 mol %, and even more preferably 50 mol %. On the other hand, the upper limit of the BTDA content is preferably 75 mol%, more preferably 65 mol%. If the BTDA content is less than the lower limit, the effect of BTDA in improving the bending workability of the insulating layer may be insufficient. Conversely, if the BTDA content exceeds the upper limit, the structure derived from BPDA cannot be sufficiently introduced into the polyimide, which is the main component of the insulating layer, and as a result, the insulating layer is resistant to moisture and heat deterioration. may decrease.

(aromatic diamine)
Examples of the aromatic diamine used as a raw material for the polyimide precursor include 4,4′-diaminodiphenyl ether (4,4′-ODA), 3,4′-diaminodiphenyl ether (3,4′-ODA), 3,3 Diaminodiphenyl ethers (ODA) such as '-diaminodiphenyl ether (3,3'-ODA), 2,4'-diaminodiphenyl ether (2,4'-ODA), 2,2'-diaminodiphenyl ether (2,2'-ODA) ), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4′-bis(4-aminophenoxy)biphenyl (BAPB), 4,4′-diaminodiphenylmethane, 3, 4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,4'-diaminodiphenylmethane, 2,2'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3, 3'-diaminodiphenyl sulfone, 2,4'-diaminodiphenyl sulfone, 2,2'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 2,4'-diaminodiphenyl sulfide, 2,2'-diaminodiphenyl sulfide, paraphenylenediamine (PPD), metaphenylenediamine, p-xylylenediamine, m-xylylenediamine, 2,2'-dimethyl- 4,4'-diaminobiphenyl, 1,5-diaminonaphthalene, 4,4'-benzophenonediamine, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl -4,4'-diaminodiphenylmethane and the like. These aromatic diamines may be used alone or in combination of two or more.

The aromatic diamine used as a raw material for the polyimide precursor preferably contains ODA, BAPP, BAPB, or a combination thereof. By using ODA as a raw material for the polyimide precursor, the toughness of the insulating layer can be improved. As the ODA, 4,4'-ODA is preferable. In addition, by using at least one of BAPP and BAPB, which have relatively large molecular weights, as a raw material for the polyimide precursor, the NMP mass swelling degree can be increased appropriately, and as a result, bending of the insulating layer You can improve your performance.

In order to effectively improve the toughness of the insulating layer, the aromatic diamine may contain only ODA among the ODA, BAPP and BAPB. In this case, the lower limit of the ODA content relative to 100 mol % of the aromatic diamine is preferably 50 mol %, more preferably 90 mol %, and even more preferably 99 mol %. Thus, by setting the ODA content to the above lower limit or more, the toughness of the insulating layer can be further improved. Further, the content of ODA is particularly preferably 100 mol %.

On the other hand, in order to improve the bending workability and toughness of the insulating layer in a well-balanced manner, the aromatic diamine preferably contains ODA and at least one of BAPP and BAPB. In this case, the lower limit of the total content of ODA, BAPP and BAPB with respect to 100 mol % of the aromatic diamine is preferably 50 mol %, more preferably 90 mol %, and even more preferably 99 mol %. Moreover, as said total content, 100 mol% is especially preferable. Furthermore, the ratio of the content of ODA in the aromatic diamine to the total content of BAPP and BAPB (content of ODA/total content of BAPP and BAPB) is, for example, 15/85 or more and 70/30 or less. can do.

The polyimide precursor may be a reaction product obtained by polymerization of an aromatic tetracarboxylic dianhydride and an aromatic diamine with other raw materials. Examples of the other raw materials include aliphatic tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic dianhydride and aliphatic diamines such as hexamethylenediamine.

The polyimide precursor is preferably a reaction product obtained substantially only from BPDA, ODA, and at least one of PMDA, BTDA, BAPP and BAPB as raw materials. That is, the polyimide, which is the main component of the insulating layer of the insulated wire, has a structure substantially derived from BPDA, a structure derived from ODA, and a structure derived from at least one of PMDA, BTDA, BAPP and BAPB. It is preferably formed only by Specifically, the lower limit of the total proportion of BPDA, ODA, PMDA, BTDA, BAPP and BAPB in all raw materials of the polyimide precursor is preferably 95 mol %, more preferably 99 mol %. Moreover, the above total ratio is most preferably 100 mol %.

In addition, it is preferable that all the insulating layers of the plurality of insulating layers contain the above-mentioned polyimide as a main component. good too. Examples of other synthetic resins that can be used include polyamideimide, polyesterimide, polyurethane, and polyetherimide.

(Method for synthesizing polyimide precursor)
The polyimide precursor can be obtained by a polymerization reaction of the aromatic tetracarboxylic dianhydride and the aromatic diamine described above. The method of the polymerization reaction can be the same as in the synthesis of conventional polyimide precursors. A specific method of the polymerization reaction includes, for example, a method of mixing an aromatic tetracarboxylic dianhydride and an aromatic diamine in an organic solvent and heating the mixed solution. By this method, the aromatic tetracarboxylic dianhydride and the aromatic diamine are polymerized, and a solution of the polyimide precursor dissolved in the organic solvent can be obtained.

The reaction conditions for the above polymerization may be appropriately set depending on the raw materials used, etc. For example, the reaction temperature can be 10° C. or higher and 100° C. or lower, and the reaction time can be 0.5 hours or longer and 24 hours or shorter.

The molar ratio of the aromatic tetracarboxylic dianhydride and the aromatic diamine used in the polymerization (aromatic tetracarboxylic dianhydride/aromatic diamine) is 100/100 from the viewpoint of efficiently proceeding the polymerization reaction. The closer to , the better. The molar ratio can be, for example, 95/105 or more and 105/95 or less.

Examples of organic solvents used in the above polymerization include aprotic polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, and γ-butyrolactone. Available. These organic solvents may be used alone or in combination of two or more. As used herein, the term "aprotic polar organic solvent" refers to a polar organic solvent that does not have a proton-releasing group.

The amount of the organic solvent used is not particularly limited as long as it is an amount that can uniformly disperse and dissolve the aromatic tetracarboxylic dianhydride and the aromatic diamine. The amount of the organic solvent used can be, for example, 100 parts by mass or more and 1,000 parts by mass or less with respect to a total of 100 parts by mass of the aromatic tetracarboxylic dianhydride and the aromatic diamine.

[Other layers]
In the insulated wire, another layer may be laminated on the outer peripheral side of one or more insulating layers. Examples of the other layer include a surface lubricating layer.

<Manufacturing method of insulated wire>
Next, an example of a suitable method for manufacturing the insulated wire will be described. The method for manufacturing the insulated wire includes a coating step of coating the outer circumference of the conductor with a resin varnish, and a heating step of heating the coated resin varnish. The resin varnish contains a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine. In the method for manufacturing the insulated wire, the coating step and the heating step are preferably repeated. According to the insulated wire manufacturing method, the insulated wire can be manufactured easily and reliably. Hereinafter, after explaining the resin varnish used in the coating step, each step will be explained.

[Resin varnish]
The resin varnish contains a polyimide precursor. Moreover, the resin varnish usually further contains an organic solvent. As the polyimide precursor contained in the resin varnish, the polyimide precursor described for the insulated wire can be used, so the description is omitted.

(Organic solvent)
The organic solvent used for the resin varnish improves the coatability of the resin varnish. Further, the resin varnish containing the organic solvent is used in the resin varnish in the second and subsequent coating steps when repeating the coating step and the heating step on the peripheral surface side of the conductor to form a plurality of insulating layers. The organic solvent slightly dissolves the polyimide of the underlying layer (insulating layer formed in the previous coating step and heating step), so that the adhesion between each layer of the plurality of insulating layers to be formed can be improved.

As the organic solvent, an aprotic polar organic solvent is preferable. Since the polyimide precursor has high solubility in an aprotic polar organic solvent, by using an aprotic polar organic solvent as the organic solvent, even when the concentration of the polyimide precursor in the resin varnish is increased, the polyimide The precursor can be reliably dissolved. In addition, by using an aprotic polar organic solvent as the organic solvent, it becomes easier to dissolve the polyimide of the underlying layer formed by the organic solvent in the resin varnish in the second and subsequent coating steps. Adhesion between each layer of the plurality of insulating layers can be further improved.

As the aprotic polar organic solvent, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, N,N- Dimethylacetamide, dimethylsulfoxide, γ-butyrolactone and combinations thereof are preferred, and NMP is more preferred.

As the organic solvent, the organic solvent used in the polymerization reaction of the polyimide precursor described above may be used as it is, or may be added separately after obtaining the polyimide precursor, but from the viewpoint of workability, the polyimide precursor It is preferable to use the organic solvent used in the polymerization reaction of (1) as it is. The content of the organic solvent in the resin varnish can be, for example, in the range of 100 parts by mass or more and 1,000 parts by mass or less with respect to 100 parts by mass of the polyimide precursor.

(other ingredients)
The resin varnish may contain various additives such as pigments, dyes, inorganic or organic fillers, lubricants, adhesion improvers, and reactive low-molecular weight compounds in addition to the components described above. Among these, by containing a melamine compound as an adhesion improver, the adhesion between the formed insulating layer and the conductor can be improved. Furthermore, the resin varnish may contain other resins within the scope of the present invention. When the resin varnish contains the above-described components, the content of the above-described components in the resin varnish may be, for example, 0.5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the polyimide precursor. .

(Method for producing resin varnish)
As a method for producing the resin varnish, for example, a method in which the polyimide precursor is dissolved in an organic solvent as described in the method for synthesizing the polyimide precursor is directly used as the resin varnish. Further, as a method for producing the resin varnish, for example, after purifying the polyimide precursor from a solution in which the polyimide precursor is dissolved in an organic solvent, the obtained purified polyimide precursor and other components such as an organic solvent are mixed. There is also a method for

[Coating process]
In this step, a resin varnish, which will be described later, is applied to the outer peripheral side of the conductor. The coating method is not particularly limited, but includes, for example, a method using a coating apparatus provided with a resin varnish tank in which the resin varnish is stored and a coating die. According to this coating apparatus, the resin varnish adheres to the outer peripheral surface of the conductor by passing the conductor through the resin varnish tank, and then the resin varnish is applied to the outer peripheral surface of the conductor with a uniform thickness by passing through the coating die. It is coated with In this step, the resin varnish may be directly applied to the outer peripheral surface of the conductor, an intermediate layer such as an adhesion improving layer is provided in advance on the outer peripheral surface of the conductor, and the resin Varnish may be applied.

When the coating step and the heating step are repeated in the method for manufacturing an insulated wire, a resin varnish other than the resin varnish described above may be used in some of the plurality of coating steps.

[Heating process]
In this step, the resin varnish coated on the conductor is heated by, for example, a method of running the conductor coated with the resin varnish in a heating furnace. By this heating step, the polyimide precursor contained in the resin varnish is imidized and volatile components such as organic solvents are removed, and an insulating layer, which is a baking layer, is laminated on the outer peripheral side of the conductor. The heating method is not particularly limited, and conventionally known methods such as hot air heating, infrared heating, and high-frequency heating can be used. The heating temperature can be, for example, 350° C. or higher and 500° C. or lower. The heating time can be, for example, 5 seconds or more and 100 seconds or less. When the conductor coated with the resin varnish is heated by running in a heating furnace, the set temperature in the heating furnace is regarded as the heating temperature, and the linear velocity of the conductor is the distance from the entrance to the exit of the heating furnace. shall be regarded as the above heating time.

Here, when the polyimide formed by the above heating step contains a large amount of crystal structure, it becomes difficult for the resin varnish solvent such as NMP to permeate between the molecules of the polyimide, so the NMP mass swelling degree of the insulating layer decreases. presumed to be easier. Therefore, in the heating step, from the viewpoint of ensuring that the NMP mass swelling degree of the insulating layer is within the above range, the following methods (A) to (C) are adopted to polyimide, which is the main component of the insulating layer. It is preferable to make it difficult to form a crystal structure. That is, in the heating step, in order to melt the crystal structure already contained at the stage where the polyimide is formed, the heating temperature is relatively high at 400 ° C. or higher and 500 ° C. or lower (A), the heating time is It is preferable to employ method (B) or the like in which the time is relatively long, such as 30 seconds or more and 100 seconds or less. In addition, in the heating step, in order to suppress the formation of a crystal structure when the above-mentioned high-temperature polyimide is cooled, the method (C) of quenching the insulating layer and the conductor immediately after heating may be adopted. Examples of the quenching method include a method of blowing air to the insulating layer and the conductor, and a method of exposing the insulating layer and the conductor to a low temperature (for example, 0° C. or higher and 15° C. or lower). However, since the degree of mass swelling can be controlled also by the type of polyimide precursor, the above methods (A) to (C) are not necessarily required.

When the coating process and the heating process are repeated in the method for manufacturing an insulated wire, the number of times the coating process and the heating process are repeated may be, for example, 2 times or more and 200 times or less.

[Other embodiments]
The above-disclosed embodiments should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is not limited to the configuration of the above-described embodiment, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims. be.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

In this example, the weight average molecular weight of the polyimide precursor was determined according to JIS-K7252-1:2008 "Plastics-Determination of the average molecular weight and molecular weight distribution of polymers by size exclusion chromatography-Part 1: General rule". was measured using gel permeation chromatography (GPC).

<Preparation of resin varnish>
[Preparation of resin varnish V1]
After dissolving 100 mol% of 4,4′-ODA in N-methyl-2-pyrrolidone, 10 mol% of PMDA and 90 mol% of 3,3′,4,4′-BPDA were added to the resulting solution, and the mixture was stirred under a nitrogen atmosphere. was stirred. Thereafter, the mixture was allowed to react at 80° C. for 3 hours while stirring, and then cooled to room temperature to prepare a resin varnish V1 in which the polyimide precursor was dissolved in N-methyl-2-pyrrolidone as an organic solvent. The polyimide precursor concentration in this resin varnish V1 was 30% by mass. Moreover, the weight average molecular weight of the polyimide precursor contained in the resin varnish V1 was 30,000.

[Preparation of resin varnishes V2 to V14]
Resin varnishes V2 to V14 were prepared in the same manner as in the preparation of resin varnish V1 except that the types and amounts of the aromatic tetracarboxylic dianhydrides and aromatic diamines were as shown in Table 1.

<Manufacture of insulated wires>
[Insulated wire No. 1 production]
A round wire composed mainly of copper and having an average diameter of 1 mm was prepared as a conductor. A step of applying the resin varnish V1 to the outer peripheral surface of the conductor and a step of heating the conductor coated with the resin varnish in a heating furnace under conditions of a heating temperature of 400° C. and a heating time of 30 seconds are repeated 10 times each. Thus, an insulated wire No. 1 comprising the above conductor and an insulating layer having an average thickness of 35 μm laminated on the outer peripheral surface of the conductor. got 1.

[Insulated wire No. Production of 2 to 14]
Insulated wire No. 1 except that resin varnishes V2 to V14 were used instead of resin varnish V1. Insulated wire no. 2-14 were produced.

[Measurement of NMP Mass Swelling Degree]
The insulating layer of the insulated wire manufactured above was stripped off with a cutter knife, and the obtained insulating layer was used as a sample. After this sample was immersed in NMP (manufactured by Mitsubishi Chemical Corporation) at 80° C. for 4 hours, the mass was measured, and this was defined as the mass R1 (g) of the insulating layer after the NMP swelling treatment. Next, after drying the sample at 200° C. for 1 hour, the mass was measured again, and this was defined as the mass R2 (g) of the insulating layer after drying. Substituting R1 and R2 into the following formula, this was taken as the NMP mass swelling degree. Table 1 shows insulated wire No. It exhibits an NMP mass swelling degree of 1-14.
NMP mass swelling degree (times) = R1/R2

<Evaluation>
Insulated wire no. 1 to 14 were used to evaluate the wet heat deterioration resistance and bending workability of the insulating layer. Table 1 shows the evaluation results.

[Damp heat deterioration resistance]
The wet heat deterioration resistance of the insulating layer was evaluated by performing wet heat treatment under conditions of 85 ° C temperature, 95% relative humidity, and 750 hours while stretching the insulated wire by 10% in the longitudinal direction, and visually observing the insulated wire after treatment. A case where no cracks were observed on the surface was rated as "A (good)", and a case where cracks were observed on the surface was rated as "B (not good)".

[Bendability]
For the bending workability of the insulating layer, the insulated wire was bent at 90° and held in that state for 10 seconds, and then the insulating layer at the bent portion was visually confirmed. ", and the case where delamination was confirmed was judged as "B (not good)".

As is clear from Table 1, No. The insulation layers of the insulated wires 1 to 4, 6 to 7 and 11 to 13 are mainly composed of polyimide derived from a polyimide precursor using a specific amount of BPDA as a raw material, and the NMP mass swelling degree is within a specific range. Therefore, bending workability and resistance to wet heat deterioration were excellent. On the other hand, No. Insulated wires 5 and 8 to 10 did not use the above specified amount of BPDA. Also, No. For the insulated wires Nos. 5, 8, 9 and 14, the NMP mass swelling degree was outside the specified range. As a result, No. The insulation layers of the insulated wires Nos. 5, 8 to 10, and 14 were poor in at least one of the resistance to deterioration by moist heat and bending workability.

The insulated wire according to one aspect of the present invention is excellent in bending workability and resistance to moisture-heat deterioration of the insulating layer.

Claims (3)

An insulated wire comprising a conductor and one or more insulating layers laminated on the outer peripheral side of the conductor,
At least one of the insulating layers is mainly composed of a polyimide derived from a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, and is immersed in N-methyl-2-pyrrolidone at 80 ° C. for 4 hours. The mass swelling degree is 1.3 times or more and 20.0 times or less when
The aromatic tetracarboxylic dianhydride comprises biphenyltetracarboxylic dianhydride,
An insulated wire, wherein the content of biphenyltetracarboxylic dianhydride is 25 mol% or more and 95 mol% or less based on 100 mol% of the aromatic tetracarboxylic dianhydride. The aromatic tetracarboxylic dianhydride further comprises pyromellitic dianhydride,
The insulated wire according to claim 1, wherein the content of pyromellitic dianhydride is 5 mol% or more and 75 mol% or less based on 100 mol% of the aromatic tetracarboxylic dianhydride. The insulated wire according to claim 1 or 2, wherein the aromatic diamine contains diaminodiphenyl ether.